I got a new ray yesterday, ordered as a t-cup, but as most are looks to be a retic and is quite an adorable young ray. I was wondering how to sex rays and what I should feed him to bulk him up?
Congratulations. It can be difficult to sex rays when they are young, males have 2 claspers just below the tail, females don't. You can see the claspers highlighted in red on this picture.
On a young ray the claspers will be much smaller and harder to spot.
Good foods for getting a ray to put on weight are nightcrawlers and if they will eat it tilapia. California blackworms are also good if your ray wants to be stubborn.
BTW, there is no such thing as a teacup ray, its just a generic term some sellers use for a stingray pup, usually retics but I have seen motoros be called teacups to.